tail: fix uninitialized memory read when failing to read file

Reproduced under UBSAN with `tail -f <&-` giving:
  tail.c:2220:18: runtime error: load of value 190,
  which is not a valid value for type ‘_Bool'

* src/tail.c (tail_file): Ensure f->ignore is initialized
in all cases where we can't tail the specified file.
* tests/tail-2/follow-stdin.sh: Add a test case which
checks stderr has no UBSAN warnings.
Fixes http://bugs.gnu.org/25041

diff --git a/src/tail.c b/src/tail.c
index 5c75be08dea155c67d35f4c73302ba769849b899..6bf1e77d03416aac26bd949a52bf388663e0cf71 100644 (file)
--- a/src/tail.c
+++ b/src/tail.c
@@ -1940,8 +1940,6 @@ tail_file (struct File_spec *f, uintmax_t n_units)
               ok = false;
               f->errnum = -1;
               f->tailable = false;
-              f->ignore = ! (reopen_inaccessible_files
-                             && follow_mode == Follow_name);
               error (0, 0, _("%s: cannot follow end of this type of file%s"),
                      quotef (pretty_name (f)),
                      f->ignore ? _("; giving up on this name") : "");
@@ -1949,6 +1947,8 @@ tail_file (struct File_spec *f, uintmax_t n_units)
 
           if (!ok)
             {
+              f->ignore = ! (reopen_inaccessible_files
+                             && follow_mode == Follow_name);
               close_fd (fd, pretty_name (f));
               f->fd = -1;
             }

diff --git a/tests/tail-2/follow-stdin.sh b/tests/tail-2/follow-stdin.sh
index a2f180428e4bb6b95e24e8a9e990cdf9294e17eb..3d51f600653270d665a0806b498cfa6638779876 100755 (executable)
--- a/tests/tail-2/follow-stdin.sh
+++ b/tests/tail-2/follow-stdin.sh
@@ -50,4 +50,16 @@ for mode in '' '---disable-inotify'; do
   cleanup_
 done
 
+
+# Before coreutils-8.26 this would induce an UMR under UBSAN
+returns_ 1 timeout 10 tail -f - <&- 2>err || fail=1
+cat <<\EOF >exp || framework_failure_
+tail: cannot fstat 'standard input': Bad file descriptor
+tail: error reading 'standard input': Bad file descriptor
+tail: no files remaining
+tail: -: Bad file descriptor
+EOF
+compare exp err || fail=1
+
+
 Exit $fail